The RE0 is more detailed but sounds lifeless as compared to the S4. The S4 has more energy and impact. Which is something I prefer because I can really get into the music without being distracted by details.

Comparing the S4 to the RE0, the S4 is definitley more active, busier. But for me, I don't get distracted with the details of the RE0 -- I DO get distracted with the sizzle of the S4, thinking "how can I tone this done some?" The RE0 is smooth enough that I can listen for extended time and to me, it stays balanced jumping from song to song, genre to genre.

Just got a pair of the S4i's and have to say am pretty impressed with the sound quality, though I have yet to burn them in completely, they've got around 10-15 hours on them. The bass is quite detailed and certainly present. I've heard a few other IEM's but my experience is not extensive, but for working with the iPhone I would definately recomend it.

Comparing the S4 to the RE0, the S4 is definitley more active, busier. But for me, I don't get distracted with the details of the RE0 -- I DO get distracted with the sizzle of the S4, thinking "how can I tone this done some?" The RE0 is smooth enough that I can listen for extended time and to me, it stays balanced jumping from song to song, genre to genre.

Well, after the suggestion that I check out the UM56s with the S4s, I would not call them un-detailed. The deep custom sleeves do give the S4s even more oomph, but in a good way.

As for sizzle, mine are well over 150 hours and with the custom tips, the sizzle sounds pretty good. Though my sizzle and your sizzle are no doubt different sizzles. LOL.I just never hear even a bit of harshness with the S4s now, unless of course the track has it already built in. Again, I've tried the RE2 and the RE3 (now RE252, but with changes other than a new name), and the details are nice. Just felt the bass was lacking and didn't want to use an amp.

For long-term listening, I had the S4s in my ears (with modded shure flanges) for eight hours the other day in a poker tournament, and never felt a bit fatigued. Just my experience. I really think they keep morphing away from any harshness until they hit the right spot somewhere over 100 hours. If you have crossed that plane, then I guess they are maybe too much for your ear sensibilities.

Small update:
I was messing with some other tips today and the S4 is a very good match with the Shure soft flex tips (mediums work best for me). I think they sound smoother than the modded bi-flanges, and are just as comfy. There is something about the S4 design that makes them comfy no matter which tip I try. I definitely don't care about trying foamies with them. For now, I will use either the Shure grey soft flex or the UM56s. And again, not hearing any harsh sounds coming from them. It's just gone.

Much of the time, during tournaments, which are long and boring for the most part. Long is good though, means you are getting to the final table. And often I have one in to just hear some music. Some of the players on TV use those silly Bose phones, or worse, guys winning millions of dollars with ibuds in their ears.

In talking about the sizzle/slight harshness during and after burn-in, do the S4's resemble the Super Fi Pro sound at all? That's how I hear SFP....pretty decent full sound all the way around but a bit harsh and unrefined....a bit fatiguing at higher volumes.